fix: prevent silent abort in piped install when interactive prompts fail (#69)

[cutepawss]

Fixes #69

Problem

The install script silently aborts when run via curl | bash on systems where sudo requires a password (e.g. fresh Debian 12 without ripgrep).

Root cause: The script uses set -e (line 16) which exits on any non-zero return code. When running via curl | bash, stdin is a pipe — not a terminal. The read -p command at line 471 (sudo package install prompt) hits EOF on the piped stdin and returns exit code 1. Under set -e, this silently kills the entire script before clone_repo, setup_path, etc. ever run.

Result: uv gets installed but hermes is never set up. No error message is shown.

Reproduction

# Simulates the exact failure:
bash -c 'set -e; echo "before read"; read -p "prompt: " -n 1 -r < /dev/null; echo "NEVER REACHED"'
# Output: "before read" then silent exit with code 1

Fix

Detect non-interactive mode at script start using the standard POSIX test [ -t 0 ] (checks if stdin is a terminal). When running in piped mode, skip all interactive prompts and show clear messages telling the user what to run manually.

if [ -t 0 ]; then
    IS_INTERACTIVE=true
else
    IS_INTERACTIVE=false
fi

This is the same approach used by rustup, nvm, and oh-my-zsh install scripts.

Guarded prompts

Location	Prompt	Non-interactive behavior
install_system_packages	sudo password for ripgrep/ffmpeg	Shows sudo apt install ... command to run manually
run_setup_wizard	interactive hermes setup	Skips, shows hermes setup to run after install
maybe_start_gateway	WhatsApp QR pairing	Skips, shows hermes whatsapp to run later
maybe_start_gateway	gateway service install	Skips, shows hermes gateway install to run later

The sudo prompt (row 1) is the direct cause of #69. The other three use the same read -p pattern and would fail identically in piped mode, so they are guarded for completeness.

Verification

# Before fix (silent abort):
bash -c 'set -e; read -p "test: " -n 1 -r < /dev/null; echo "OK"'
# Output: (nothing) — exit code 1

# After fix (completes successfully):
bash -c 'set -e; if [ -t 0 ]; then read -p "test: " -n 1 -r; else echo "skipped"; fi; echo "OK"' < /dev/null
# Output: "skipped" then "OK" — exit code 0

Scope

Single file: scripts/install.sh. No changes to Python code or agent behavior. Normal interactive installs (bash install.sh) are completely unaffected — the prompts work exactly as before when stdin is a terminal.